In recent years there has seen a tremendous increase in the demand for wireless networks capable of handling data communications. In order to accommodate this increased demand there is a constant search to find improved, more efficient approaches to communicating data. One such approach has been to suggest multiple rates for communicating data. In the case of voice communications this is primarily important in permitting a higher quality signal for those units having the higher data rates, although in some systems it may also permit increased loading by having users go to lower rates (and hence produce somewhat lower interference levels). In non-voice data communications the concerns are somewhat different. Because the data rate directly effects the throughput, most users will prefer to use a higher rate, thus keeping air/billing time to a minimum. However, system flexibility is still desirable, allowing for lower rates to be used for channels suffering from higher levels of interference, thus permitting increased correction coding rates to be employed.
One limitation of current or proposed multirate coding schemes is that the rate is typically established at the beginning of a communications session. While this may be fine for a more or less stationary remote unit, it does not allow for changes in moving remote units or the surrounding environment. Thus, for example, if a user were to initiate a file transfer from a PDA (personal digital assistant), which finally received an allocation right before entering a shadowed region (turning a corner behind a building, entering a tunnel, etc.) a higher data rate would typically be negotiated. But, because the majority of the communication session would occur in the shadowed region, the continued use of the higher data rate will lead to a higher error and repeat transmission rate. Similarly, if the user were to start communications within a shadowed region, say a parking garage, but the majority of the session was completed in a good quality coverage zone, significantly more time will be required than actually needed to complete the data transfer. This is disadvantageous both to the user, who pays more, and the operator, who's limited channel resources are tied up needlessly, even potentially blocking higher priority uses. Finally, as both examples indicate, where multiple users having quite different channel characteristics are accessing the same communication channel, a single rate applied to both such as done in prior art systems is at best a compromise detrimentally effecting both users.
There remains therefore a need for an improved means for providing multirate data communications in wireless systems that solves these and related problems.